Christian König <christian.koenig@xxxxxxx> writes:
> Am 27.04.2017 um 18:17 schrieb Nikola Pajkovsky:
>> This is super simple elimination of else branch and I should
>> probably even use unlikely in
>>
>> if (ring->count_dw < count_dw) {
>>
>> However, amdgpu_ring_write() has similar if condition, but does not
>> return after DRM_ERROR and it looks suspicious. On error, we still
>> adding v to ring and keeping count_dw-- below zero.
>>
>> if (ring->count_dw <= 0)
>> DRM_ERROR("amdgpu: writing more dwords to the ring than expected!\n");
>> ring->ring[ring->wptr++] = v;
>> ring->wptr &= ring->ptr_mask;
>> ring->count_dw--;
>>
>> I can obviously be totaly wrong. Hmm?
>
> That's just choosing the lesser evil.
>
> When we write more DW to the ring than expected it is possible (but
> not likely) that we override stuff on the ring buffer which is still
> executed by the command processor leading to a possible CP crash.
>
> But when we completely drop the write the commands in the ring buffer
> will certainly be invalid and so the CP will certainly crash sooner or
> later.
Instead of choosing the lesser evil, is there good way to design ring
buffer right way?
> Please add the unlikely() as well and then send out the patch with a
> signed-of-by line and I will be happy to push it into our upstream
> branch.
Proper patch has been sent.
--
Nikola
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